This study represents a continuation of work on an evaluation of macromolecular interactions in the E. coli ribosome. The study consists of a characterization of isolated proteins from the subunits employing chromatographic and hydrodynamic techniques. The purified and characterized proteins are examined singularly and in mixtures for evidence of macromolecular interactions by analytical ultracentrifuge sedimentation equilibrium experiments. The resultant data being of the form refractive index distribution from interference optics or chromophoric distribution from absorption optics is analyzed by developed numerical procedures to reveal the presence of molecular complex that may or may not be in reversible equilibrium. The combination of the two optical methods may in some instances allow for an evaluation of systems containing three protein species when certain assumptions are made regarding pairwise interactions. In addition to many proteins from the small subunit the large subunit proteins L7/L12 and L10 are being evaluated for specific interaction as a function of temperature in an effort to understand the nature of that complex from a thermodynamic analysis. It is hoped that through these studies a map can be constructed which illustrates where within the structure of the subunits resides the principal interactions responsible for their integrity.